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PHYS 1444 – Section 004 Lecture #1

PHYS 1444 – Section 004 Lecture #1. Monday Jan 22, 2007 Dr. Andrew Brandt. Syllabus and Introduction Chapter 21 -Static Electricity and Charge Conservation -Charges in Atom, Insulators and Conductors & Induced Charge -Coulomb’s Law.

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PHYS 1444 – Section 004 Lecture #1

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  1. PHYS 1444 – Section 004 Lecture #1 Monday Jan 22, 2007 Dr. Andrew Brandt • Syllabus and Introduction • Chapter 21 • -Static Electricity and Charge Conservation • -Charges in Atom, Insulators and Conductors & • Induced Charge • -Coulomb’s Law Please turn off your cell-phones, pagers and laptops in class Thanks to Dr. Yu for bringing this class into 21st Century! PHYS 1444-004, Spring 2007 Dr. Andrew Brandt

  2. Who am I? • Name: Andrew Brandt (You can call meDr. Brandt) • Office: Rm 344, CPB (Physics and Chemistry Building) • Extension: x2706, E-mail: brandta@uta.edu • Education: B.S. Physics/Economics College of William and Mary 1985; Ph. D. 1992 UCLA • My Research Area: High Energy Physics (HEP) • Collide particles (currently protons and anti-protons) at energies equivalent to 10 Quadrillion degrees • To understand • Fundamental constituents of matter • Interactions or forces between the constituents • A pure scientific research activity • Applied use of the fundamental laws not always obvious, but use of discovery of electron was not immediately known either! • Indirect product of research contribute to every day lives; eg. WWW

  3. Matter Molecule Atom Nucleus Baryon Quark (Hadron) u Electron (Lepton) High Energy Physics Structure of Matter 10-14m 10-9m 10-10m 10-15m <10-19m 10-2m Condensed matter/Nano-Science/Chemistry protons, neutrons, mesons, etc. p,W,L... top, bottom, charm, strange, up, down Atomic Physics Nuclear Physics <10-18m

  4. Discovered in 1995 Directly observed in 2000 The Standard Model • Assumes the following fundamental structure:

  5. Chicago  CDF p DØ Tevatron p Fermilab Tevatron and LHC at CERN • World’s Highest Energy proton-proton collider in 2 years • Ecm=14 TeV (=44x10-7J/p 1000M Joules on 10-4m2) • Equivalent to the kinetic energy of a 20t truck at a speed 212 mi/hr • Present Highest Energy proton-anti-proton collider • Ecm=1.96 TeV (=6.3x10-7J/p 13M Joules on 10-4m2) • Equivalent to the kinetic energy of a 20t truck at a speed 80 mi/hr

  6. 30’ 30’ 50’ DØ Detector: Run II • Weighs 5000 tons • Can inspect 3,000,000 collisions/second • Records 50 collisions/second • Records ~12.5M Bytes/second • Will record 2 Peta bytes in the current run. • Has over a 100 million parts

  7. How does an Event Look in a Collider Detector? Highest ET dijet event at DØ CH “calorimeter jet” hadrons FH  EM “particle jet” Time “parton jet”

  8. High Energy Art

  9. p Forward Proton Detector Layout p P1U P2O Q4 Q3 Q2 Q2 S D Q3 Q4 S A1 D1 A2 D2 P1D P2I • 9 momentum spectrometers comprised of 18 Roman Pots • Scintillating fiber detectors (built at UTA) are moved close (~6 mm) to the beam to track scattered protons and anti-protons • Reconstructed track is used to calculate momentum and scattering angle, covering new kinematic regions • Allows combination of tracks with high momentum scattering in the central detector Veto 57 59 23 0 33 23 33 Z(m) Former UTAgraduate student Michael Strang

  10. proton Fast Timing Detectors for ATLAS WHO? UTA (Brandt), Alberta, Louvain, FNAL WHY? Background Rejection Ex, Two protons from one interaction and two b-jets from another How? Use timing to measure vertex photon How Fast? 10 picoseconds (light travels 3mm in 10 psec!)

  11. Primary Web Page http://www-hep.uta.edu/~brandta/teaching/sp2007/teaching.html

  12. Grading • Exams: 50% • Best two of three exams (2 midterms + final) • Comprehensive final • Exams will be curved if necessary • No makeup tests • Homework: 20% (no late homework) • Pop quizzes10% • Lab score: 20%

  13. Homework Solving homework problems is the best (only?) way to comprehend class material An electronic homework system has been setup for you Details are in the syllabus and on web (class id 14445 everyone needs their own UT EID) https://hw.utexas.edu/ 2 points extra credit on final HW grade if registered by class 1/24/07, 1 point if 1/29/07 (first hw on Ch. 21 will be due Wednesday 1/31/07 at 12 pm) Each homework carries the same weight Your lowest two homework scores will be dropped Home work will constitute 20% of the total A good way of keeping your grades high Allowed (encouraged) to work with others and get help from physics clinic as needed—always attempt homework first on your own, or you will likely pay for it on the tests (DON’T COPY!)

  14. Getting Started with On-line Homework STEP 1:   Go to the Homework Service at the URL    https://hw.utexas.edu/Select the link Register yourself in your class   Unique number: 14445STEP 2:   Return to https://hw.utexas.edu/Download: Students' Instructions Download:     First Homework    STEP 3:   Work one question and submit its answer before the next class period. STEP 4:   Continue submitting answers until due time. STEP 5:   Download solutions after due time.

  15. Homework Scoring VII. Scoring a) Multiple-choice questions A randomly guessing student should, on average, receive the same score as a student who does not answer. Our multiple-choice scoring scheme corrects for random guessing by giving negative scores for incorrect answers. (The SAT does this also.) This scheme makes haphazard guessing a waste of time, which will not improve (or help) your score over the long run. If you are not sure of the correct answer, but you can eliminate one or more of the choices as wrong, you increase your chances of selecting the correct answer. Statistically, it is to your advantage to answer such a question. b) Numeric questions For more than one try, the full credit score is multiplied by 0.93 ^ (t - 1), where "t" is the number of tries that you use, and the "^" is notation for "to the power of." (Note: 0.93 ^ 0 = 1.) maximum of 7

  16. Attendance and Class Style • Attendance: • is STRONGLY encouraged, but I will not generally take attendence • Class style: • Lectures will be primarily on electronic media • The lecture notes will be posted AFTER each class • Will be mixed with traditional methods • Active participation through questions and discussion are STRONGLY encouraged

  17. Why Do Physics? Exp.{ Theory { • To understand nature through experimental observations and measurements (Research) • Establish limited number of fundamental laws, usually with mathematical expressions • Explain and predict nature • Theory and Experiment work hand-in-hand • Theory generally works under restricted conditions • Discrepancies between experimental measurements and theory are good for improvement of theory • Modern society is based on technology derived from detailed understanding of physics

  18. What do you want from this class? I want an “A” I just want to pass! I want you to: • Understand fundamental principles of E&M • Learn how to do research and analyze what you observe • Learn how to express observations and measurements in mathematical language • Learn how solve problems

  19. Brief History of Physics • AD 18th century: • Newton’s Classical Mechanics: A theory of mechanics based on observations and measurements • AD 19th Century: • Electricity, Magnetism, and Thermodynamics • Late AD 19th and early 20th century (Modern Physics Era) • Einstein’s theory of relativity: Generalized theory of space, time, and energy (mechanics) • Quantum Mechanics: Theory of atomic phenomena (small distance scales) • Physics has come very far, very fast, and is still progressing, yet we’ve got a long way to go • What is matter made of? • How does matter get mass? • How and why do particles interact with each other? • How is universe created?

  20. Need for Standards and Units • Three basic quantities for physical measurements • Length, Mass, and Time • Need a language so that people can understand each other (How far is it to Chicago? 1000) • Consistency is crucial for physical measurements • The same quantity measured by one person must be comprehensible and reproducible by others • A system of unit called SI (SystemInternational) established in 1960 • Length in meters (m) • Mass in kilo-grams (kg) • Time in seconds (s)

  21. SI Base Quantities and Units

  22. deci (d): 10-1 centi (c): 10-2 milli (m): 10-3 micro (m): 10-6 nano (n): 10-9 pico (p): 10-12 femto (f): 10-15 atto (a): 10-18 Prefixes and their meanings • deca (da): 101 • hecto (h): 102 • kilo (k): 103 • mega (M): 106 • giga (G): 109 • tera (T): 1012 • peta (P): 1015 • exa (E): 1018

  23. Examples 1.3 and 1.4 for Unit Conversions • Ex 1.3: A silicon chip has an area of 1.25in2. Express this in cm2. • Ex 1.4: Where the posted speed limit is 65 miles per hour (mi/h or mph), what is this speed (a) in meters per second (m/s) and (b) kilometers per hour (km/h)? (a) Oops, what about sig. figs.? (b)

  24. { Systematic Uncertainties • Physical measurements have limited precision, no matter how good they are, due to: Number of measurements Quality of instruments (meter stick vs micrometer) Experience of the person doing measurements Etc. In many cases, uncertainties are more important and difficult to estimate than the central (or mean) values Statistical {

  25. Significant Figures • Significant figures denote the precision of the measured values • Significant figures: non-zero numbers or zeros that are not place-holders • 34 has two significant digits; 34.2 has 3; 0.001 has one because the 0’s before 1 are place holders, 34.100 has 5, because the 0’s after 1 indicates that the numbers in these digits are indeed 0’s. • When there are many 0’s, use scientific notation: • 31400000=3.14x107 • 0.00012=1.2x10-4

  26. Significant Figures • Operational rules: • Addition or subtraction: Keep the smallest number ofdecimal places in the result, independent of the number of significant digits: 34.001+120.1=154.1 • Multiplication or Division: Keep the number of significant figures of the operand with the least S.F. in the result: 34.001x120.1 = 4083, because the smallest number of significant figures is 4. • For homework service keep 4 figures to be on the safe side

  27. Static Electricity; Electric Charge and Its Conservation • Electricity is from Greek word elecktron=amber, a petrified tree resin that attracts matter if rubbed • Static Electricity: an amber effect • An object becomes charged or “posses a net electric charge” due to rubbing • Example: Rub feet on carpet and zap your little sister • Two types of electric charge • Like charges repel while unlike charges attract • Benjamin Franklin referred to the charge on a glass rod as the positive, arbitrarily. Thus the charge that attracts a glass rod is negative.  This convention is still used.

  28. Static Electricity; Electric Charge and Its Conservation • Franklin argued that when a certain amount of charge is produced on one body in a process, an equal amount of opposite type of charge is produced on another body. • The positive and negative are treated algebraically so that during any process the net change in the amount of produced charge is 0. • When you comb your hair with a plastic comb, the comb acquires a negative charge and the hair an equal amount of positive charge. • This is the law of conservation of electric charge. • The net amount of electric charge produced in any process is ZERO!! • If one object or one region of space acquires a positive charge, then an equal amount of negative charge will be found in neighboring areas or objects. • No violations have ever been observed. • This conservation law is as firmly established as that of energy or momentum.

  29. Electric Charge in the Atom • It has been understood through the past century that an atom consists of • A positively charged heavy core  What is the name? • This core is nucleus and consists of neutrons and protons. • Many negatively charged light particles surround the core  What is the name of these light particles? • These are called electrons • How many of these? • So what is the net electrical charge of an atom? • Zero!!! Electrically neutral!!! • Can you explain what happens when a comb is rubbed on a towel? • Electrons from towel get transferred to the comb, making the comb negatively charged while leaving positive ions on the towel. • These charges eventually get neutralized primarily by water molecules in the air. As many as the number of protons!!

  30. Insulators and Conductors • Let’s imagine two metal balls, one of which is charged • What will happen if they are connected by • A metallic object? • Charge is transferred, until the charge is evenly distributed • These objects are called conductors of electricity. • A wooden object? • No charge is transferred • These objects are called nonconductors or insulators. • Metals are generally good conductors whereas most other materials are insulators. • A third kind of materials called semi-conductors, like silicon or germanium  conduct only in certain conditions • Atomically, conductors have loosely bound electrons while insulators have tightly bound electrons!

  31. Induced Charge • When a positively charged metal object is brought close to an uncharged metal object • If the objects touch each other, the free electrons in the neutral ones are attracted to the positively charged object and some will pass over to it, leaving the neutral object positively charged. • If the objects get close, the free electrons in the neutral object still move within the metal toward the charged object leaving the opposite end of the object positively charged. • The charges have been “induced” in the opposite ends of the object.

  32. ground Induced Charge • We can induce a net charge on a metal object by connecting a wire to ground. • The object is “grounded” or “earthed”. • Since it is so large and conducts, the Earth can give or accept charge. • The Earth acts as a reservoir for charge. • If the negative charge is brought close to a neutral metal rod • Positive charges in the neutral rod will be attracted by the negatively charged metal. • The negative charges in the neutral metal will gather on the opposite side, transferring through the wire to the Earth. • If the wire is cut, the metal bar has net positive charge. • An electroscope is a device that can be used for measuring charge • How does this work?

  33. Coulomb’s Law • Charges exert force to each other. What factors affect the magnitude of this force? • Charles Coulomb figured this out in 1780’s. • Coulomb found that the electrical force is • Proportional to the product of the two charges • If one of the charges is doubled, the force doubles. • If both of the charges are doubled, the force quadruples. • Inversely proportional to the square of the distances between them. • Electric charge is a fundamental property of matter, just like mass. • How would you put the above into a formula?

  34. Coulomb’s Law – The Formula Formula • Is Coulomb force a scalar quantity or a vector quantity? Unit? • A vector quantity. Newtons • Direction of electric (Coulomb) force is always along the line joining the two objects. • If two charges have the same sign: forces are directed away from each other. • If two charges are of opposite sign: forces are directed toward each other. • Coulomb force is precise to 1 part in 1016. • Unit of charge is called Coulomb, C, in SI. • The value of the proportionality constant, k, in SI unit is • Thus, if two 1C charges were placed 1m apart the force would be 9x109N.

  35. Announcements • Reading assignment #1: Read Ch. 21 and Appendix A by Wes., Jan. 24 • Remember to register for homework service • No programmable calculators or cell phones allowed in class on test dates

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